The present invention relates to an environmentally safe cleaning composition and a method for removal of contaminants from a substrate surface. More particularly the present invention relates to a cleaning composition and a method for removal of solder flux from a surface of a printed circuit board.
Prior to a soldering operation for attachment of components to printed circuit boards it is conventional and essential to apply a soldering flux to insure an adherent, electrically conductive bond of solder. The printed circuit board may be protected with a solder mask which covers all areas of the substrate except where solder is to contact and adhere to a conductive surface portion. Application of flux and solder can be done by hand, wave or reflow methods. In wave soldering, the substrate is mechanically conveyed over and contacted with the flux and then with a molten solder wave. The solder adheres to all conductive surfaces on the substrate except where solder mask is present. In reflow soldering a solder paste, containing both flux and solder metal in powder form, is applied only to the points where solder bonds are to be made. Components are set in place and the entire printed circuit board assembly is heated to melt the solder. Flux which remains on the assembly after soldering can cause premature failure of the electrical circuitry through corrosion, absorption of water and other effects and must be removed.
In Hayes et al., U.S. Pat. No. 4,640,719, use of terpene compounds is disclosed in cleaning printed wiring boards. This patent discloses cleaning of residual flux and particularly rosin solder flux and adhesive tape residues employing terpene compounds such as pinene including its alpha and beta isomer, gamma terpinene, delta-3-carene, limonene and dipentene with limonene and dipentene preferred. Dipentene is the racemic mixture of the limonene optically active isomers. This patent further discloses that these terpene compounds are almost completely insoluble in water and cannot be directly flushed away by water. Therefore, in a preferred embodiment terpene compounds are combined with one or more emulsifying surfactants capable of emulsifying terpenes with water to facilitate their removal.
Dishart et al., U.S. Pat. No. 4,867,800 discloses cleaning of printed circuit board substrates with a combination of a dibasic ester and terpene.
Futch et al., U.S. Pat. No. 4,934,391 discloses removal of rosin solder flux or resist residues employing a dibasic ester and an emulsifying surfactant. In a distinct embodiment, a combination of terpenes and dibasic esters are disclosed.
With the advent of tightened restrictions on the use of CFCs and chlorocarbon solvents, metal fabricators and other manufacturers are faced with a choice among many options for satisfying their cleaning requirements. These include flammable alcohols, high-flash-point solvents, semi-aqueous cleaners based on terpenes or terpenes/dibasic esters, and aqueous cleaners. Alcohols clean well but are flammable, high-flash-point solvents leave residues which are slow drying, terpenes have undesirably low flash points and objectionable odors, dibasic esters are too aggressive for many electronics applications and sometimes attack components, and aqueous cleaners are ineffective for removing heavy oils and greases from tight clearances.